In a typical inkjet printing system, an inkjet printhead ejects fluid (e.g., ink) droplets through a plurality of nozzles toward a print medium, such as a sheet of paper, to print an image onto the print medium. The nozzles are generally arranged in one or more arrays, such that properly sequenced ejection of ink from the nozzles causes characters or other images to be printed on the print medium as the printhead and the print medium are moved relative to each other.
Thermal bubble-type inkjet printheads eject droplets of fluid from a nozzle by passing electrical current through a heating element which generates heat and vaporizes a small portion of the fluid within a firing chamber. The current is supplied as a pulse which lasts on the order of 2 micro-seconds. When a current pulse is supplied, the heat generated by the heating element creates a rapidly expanding vapor bubble that forces a small droplet out of the firing chamber nozzle. When the heating element cools, the vapor bubble quickly collapses. The collapsing vapor bubble draws more fluid from a reservoir into the firing chamber in preparation for ejecting another drop from the nozzle.
Unfortunately, because the ejection process is repeated thousands of times per second during printing, the collapsing vapor bubbles also have the adverse effect of damaging the heating element. The repeated collapsing of the vapor bubbles leads to cavitation damage to the surface material that coats the heating element. Each of the millions of collapse events ablates the coating material. Once ink penetrates the surface material coating the heating element and contacts the hot, high voltage resistor surface, rapid corrosion and physical destruction of the resistor soon follows, rendering the heating element ineffective.